1. Field of the Invention
The present invention relates to a transporting machine for transporting, for example, thin plate-like wafers.
2. Description of the Related Art
In a process of manufacturing an IC (semiconductor integrated circuit), after a wafer process of building an IC circuit onto a silicon wafer (including diffusion process, etching process, and photolithography process), an assembly process (including back surface grinding process, inspection process, and assembling process) is performed.
In the inspection process in the assembly process, an inspection machine in which a microscope and the like are mounted is used to inspect basic function and characteristics as IC, thereby judging acceptability of a chip.
The silicon wafer, which has undergone the diffusion process and left as it is, has a problem such as high electrical resistance on the back surface due residual oxide thereof.
Therefore, the silicon wafer which has completed the diffusion process is polished or ground to several hundreds μm in the back surface grinding (back grind) process.
The plurality of silicon wafers ground to be thin in the back surface grinding process is accommodated in a dedicated wafer carrier (cassette) having partitions (slits) provided at small intervals.
In the inspection process, when the thin silicon wafer accommodated in the wafer carrier is taken out to be placed on an inspection table (stage) of a microscope or the like, a dedicated transporting machine called a wafer loader is used.
Conventionally, a technique of transporting the thin silicon wafer is suggested in the description of JP 11-71025 A.
According to the description of JP 11-71025 A, there is suggested a technique in which a pair of support bars arranged in parallel to each other are used, thereby reducing bending of a wafer due to its own weight caused when the wafer is transported by a transporting arm having a center coinciding with a center of gravity of the wafer.
Even in a case of using the transporting machine as described above, difficulty in handling the silicon wafer ground to be thin to several hundreds μm in the back surface grinding process makes it difficult to increase yield in the manufacturing process.
The applicant of the present invention has found that a factor to inhibit increase of the yield is vibration of the silicon wafer resulting from static electricity with which the silicon wafer and a transporting arm (support bar) for supporting the silicon wafer are charged.
Specifically, a silicon wafer may be charged with a large amount of static electricity in operations in the wafer process and assembly process.
In a case where a wafer, which is charged by static electricity and contained in a wafer carrier formed of an insulating material, is transported by a transporting arm (support bar) at floating state, which is in turn charged to the same potential as the wafer, a repulsive force acts between the silicon wafer and the transporting arm. Then vibration is caused in the silicon wafer due to the repulsive force (repelling force).
When large vibration occurs during transportation due to the repulsive force, the wafer comes into contact with a partition portion and the like of the carrier and breaks, thereby reducing the yield in the manufacturing process.